(Reuters) – A locked switch is being blamed for the collision between an Amtrak passenger train and a freight train that killed two people and injured more than 100 others in South Carolina early on Sunday.

The head of the National Transportation Safety Board said a switch on the tracks, which the freight hauler CSX Corp. owns and operates, was padlocked in a position that steered the Amtrak train onto a siding near Columbia, S.C., where it crashed into a parked, unoccupied CSX train.

“Key to this investigation is learning why the switch was lined that way,” Robert Sumwalt, the chairman of the NTSB, told reporters at a news conference on Sunday. NTSB officials were not immediately available to elaborate.

Amtrak President and Chief Executive Richard Anderson told reporters Sunday that CSX was responsible for the wreck because of the locked switch. CSX officials were not available for comment.

Officials from both companies expressed condolences to the families of the two people killed, an Amtrak engineer and a conductor.

Two of the 116 people injured remained in critical condition overnight, officials said. Specifics were not available.

A team from the NTSB is expected to be on the scene for five to seven days. No probable cause will be issued at that time, the agency told media outlets.

(Reporting by Rich McKay, editing by Larry King)